A team of CSIRO scientists have demonstrated that a greater understanding of the chemical and physical properties of orebodies can have huge benefits. Tim Treadgold investigates what this means for exploration, mine life and mineral processing.

Long-ranked as one of Australia’s biggest sources of gold, the Plutonic gold mine in Western Australia is unique in a number of ways that set it apart from other mines in the region.

Those differences, including a peculiar location at the edge of a traditional mineral-rich ‘greenstone’ sequence of rocks, has led to a number of theories about the geological process behind the formation of the Plutonic orebody.

A more intimate understanding of the chemical and physical properties of the gold-bearing system has evolved.

Researchers have pulled together a vast array of data from multiple sources to produce a single three-dimensional model for the first time, which is helping the mine operator achieve enhanced productivity across the value chain.

One of the significant discoveries came with a fresh look at the timing of the deposition of gold in the system with a previous theory that the gold phase occurred early in the process being superseded by a model that shows the gold phase occurring much later.

While timing in a geological process may not seem important, it has led to fresh thinking about how gold in the Plutonic system can be identified and later recovered.

Potentially, the work will open new perspectives for explorers in parts of Western Australia while also enhancing the productivity of the existing Plutonic mine with major benefits from the incorporation of a gravity separation plant to recover free gold in the early stages of processing ore.

Low cost and simple to operate, a gravity circuit at the start of mineral recovery causes ‘heavy’ gold that has been liberated during the crushing phase to drop out of the ore stream. This means that less ore goes into the more complex phases of processing, effectively reducing the use of expensive chemicals and lowering power use.

Investigations into the feasibility of a gravity separation plant at Plutonic is high on the agenda of the mine’s new owner, Northern Star Resources, which is in the process of acquiring it from the Canadian-based Barrick Mines.

Northern Star Chief Executive, Bill Beament, who worked at Plutonic for eight years and spent two years as mine manager when it was owned by Barrick, is strongly in favour of gravity separation as a key component of gold processing.

‘We’ll certainly be looking closely at the CSIRO report when we take control of Plutonic,’ Mr Beament says.

Dr Guilllaume Duclaux, a senior research scientist at CSIRO, say understanding the formation of the Plutonic system is important because it could enhance the efficiency of both mining and ore processing.

The CSIRO team studied the Plutonic structure from its overall setting as measured in square kilometres down to micro-scale using tools as sensitive as the proton-induced x-ray emission probe in Melbourne and the high resolution x-ray computed tomography scanner in Perth.

‘We have looked at the fine micro-chemistry to see what elements are associated with the gold, and we have looked across the project to understand the drivers that brought the gold into the system,’ Dr Duclaux says.

‘A detailed understanding is important because if you know exactly where the gold sits on the smaller scale you will clearly improve the processing.

‘What we found by looking at the micro-scale is that many of the free gold grains could be liberated by gravity separation.

‘One of the primary aims of this project was to work across the value chain at Plutonic and we have worked with the exploration geologists to get a greater understanding of the chemistry in the rocks and with the processing managers to enhance gold recovery.

‘We have been using very advanced tools across a wide spectrum of science to understand what’s going on at the micro scale, to help understand the big picture and improve productivity.’

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